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Discussion in 'Loudspeakers' started by Seth=L, Mar 8, 2007.
Well, what does it mean,.....Peng?
It is not a simple term to break down but I can give it a shot. It is basically a measurement of the rate at which electricity can flow through the electromagnetic circuit. The lower the number (in mH or milihenries) the faster the flow. This specification is usually somewhat indicative of a driver's transient response. The faster electricity flows through a circuit the faster it can react to changes. I hope that helps a little.
It does, I understand now. Peng was talking about Klipsch and how they often have higher inductance than other speakers on average, not sure what his exact words were but it was along those lines.
If I am wrong, I am sure he will correct me.
Actually I did not make any statement that Klipsch speakers have higher inductance than others. I do not really know for sure. That's why I used the words "May be". I was only surmising, based on reports by their owners that they were getting day and night kind of improvements after they added a more powerful amp to their receivers, despite the generally higher sensitivities specified by those Klipsch speakers.
While I don't know anything about the specifications of Klipsch speakers, I do know the part of the electrical theory that tells me not all 4 ohm nominal speakers are created equal in terms of how power hungry they are. I can list a couple of reasons (I am sure there are more), such as:
1) Those nominal ratings are for impedance, not resistance. They give us a general idea as to whether our amps can deal with the load, but in extreme cases, this information (nominal impedance) alone is not enough for us to achieve optimum performance because it does not tell us the shape of the curves for resistance (R) versus frequency and inductive reactance (XL) versus frequency.
2) The formula that everyone knows are: V=IR (Ohm's law), P=VI, P=(I^2)R, or P=(V^2)/R, but in fact, V=IZ, where Z is impedance and Z=R+jXL, for simplicity, let's assume for now the capacitive reactance is negligible (it really isn't always negligible), where XL is the inductive reactance and j is the term used in complex numbers to denote the imaginary part of the vector/phasor that is shifted 90 degrees from the real term (R). V=IR is true for a purely resistive load but in some extreme cases, we should realize that in fact V=IZ, and P=VIcosΦ, Φ is the angle between the voltage phasor V and the current phasor I.
3) Consider the following two speakers with fictitious impedance as follow:
Speaker A: R=2 ohms, XL=4.58 ohms (90 degrees shifted from R)
Speaker B: R=4 ohms, X=0 ohms
In this example you can see that both speakers have 4 ohm impedance, say for a narrow bandwidth of 1 to 2K (again fictitious). Speaker A is inductive, having both the resistive and inductive components, whereas B is purely resistive. And you can see that for an amp to deliver the same 100W real power (not reactive power) into speaker A, P=(I^2)X2, but for speaker B, P=(I^2)X4. So you can see that speaker A will have to draw double the current of what speaker B will draw, hence more difficult to drive. To understand why the inductive reactance does not consume real power (Watts), remember that Power=VIcosineΦ, where Φ is the phase angle between the voltage phasor and the current phasor, for a purely inductive load this angle is 90 degree and cosine 90 degree is zero. Hence the more inductive the load is, the more current it will draw for the same power consumption.
I know little about the design of loudspeakers. I am only trying to show you that at least in theory, some 4 ohm speakers could be much more demanding than others. It depends at least on how they differ in their impedance swing and how inductive they are. To muddy the water some more, please be reminded that the impedance characteristics of loudspeakers also varies with frequencies so it is not as simple as applying the famous Ohm's law and the power formula. By impedance characteristics I mean at least:
1) resistive in nature, R versus frequency
2) inductive in nature XL versus frequency
3) capacitive in nature Xc versus frequency
For a physical resistor and inductor, the resistance of the resistor does not change with frequency except for a little bit changes due to skin effect at very high frequencies, whereas the reactance of an inductor would vary with frequency, the higher the freq. the higher the ohms. For loudspeakers, being complex and dynamic in nature, I believe both 1) and 2) vary continuously with the music signal. A nominal impedance of 8 ohms or 4 ohms gives us a general idea and is good enough most of the time but not everytime! One cautionary note, if you measure the impedance across the speaker terminals with an ohmmeter, you will get a lower value than the nominal value specified because you will be measuring its d.c. resistance. The ohmmeter's output is d.c., from its internal battery.
In a hopefully less convoluted way, I thought I should have summarize it by saying:
Given two speakers, both with impedance of 8 ohms at the same frequency, the amplifier will have to develop a higher output voltage that allows it to deliver a higher current to the speaker that has an impedance that has a higher inductive component in it, in order to develop the same watts as it will develop in the speakers that has a less inductive component in its impedance.
And in English, "There's no such thing as an amp that's TOO powerful."
(while making Tim "The Tool Man" Taylor grunts)
And if you burn up your speakers, time to buy BIGGER ones
(BTW- Great explanation PENG)
http://sound.westhost.com/cables-p5.htm#High Current Amplifiers
The first one links to a very good explanation of the impedance characteristics of loudspeakers. I included the second link just so people don't have to wonder if they need a 500WPC "high current" amp.
Does anyone know what this ESP site is all about? I read several of the articles there and I am impressed. Not only they cover the practical side well, but even on the theory side they are as good as college/university text books.
I will have to do some reading to fully understand all this, but thank you gentlemen, very much.